If you want to create a patch with svn you only
have to type in the terminal something like:

svn diff yourproject > yourproject.patch

Where yourproject is the folder containing the modified
source code.

Then, to restore the patch (apply the changes stored in
patch in a new working copy), copy the patch file
yourproject.patch in the machine where you want apply
the patch and "cd "to the parent folder
containing the yourproject folder (not inside
yourproject). Then type:

patch -p0 -i /path/to/yourproject.patch

If you do not respect the same hierarchy when creating and
applying the patch then you'll have to play around with the "p0"
parameter (gives the entire file name unmodified). Of course the
patch command is not related to SVN and you can use it in many
other environments.

Without subversion

If you are not a subversion user this is how general patchind is
done: